Predicting Crack Initiation of Solder Joints with Varying Sizes Under Bending
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The critical strain energy release rate for crack initiation, Jci, was measured under mode I loading for SAC305 solder joints between two copper substrates. Fracture tests were performed using double cantilever beam specimens at a strain rate of 0.03 s−1. Different bond-line widths (i.e., joint size in the out-of-plane dimension) and thicknesses, were examined. The fracture force per unit width and Jci (the average value of four J-integral contours encircling the crack tip) were relatively insensitive to the width of the joint ranging from 8 mm to 21 mm. Variations in bond-line thickness (i.e., 150 μm, 250 μm and 450 μm) also had an insignificant influence on the fracture energy of solder joints. This behavior was explained in terms of stress distribution, crack-tip plastic zone area and triaxiality factor produced in the solder layer. Crack initiation in the specimens was then predicted using Jci as a property. Finally, a cohesive zone model was developed using a single set of parameters that was successfully used to predict the fracture loads of the joints with different sizes.
KeywordsSolder joint joint width joint thickness fracture critical strain energy release rate constraint
List of Symbols
Applied force on the specimen
Fracture force of the specimen
Fatigue threshold strain energy release rate
Analytical critical strain energy release rate for crack initiation
Analytical steady-state critical strain energy release rate
Elastic–plastic critical strain energy release rate for crack initiation
Elastic–plastic steady state critical strain energy release rate
Critical mode I energy in cohesive region
Mode II stress intensity factor
Mode I stress intensity factor
Cohesive interface stiffness in normal direction
Solder joint thickness
Solder joint width
Phase angle (mode ratio) of loading
Cohesive normal stress
Critical cohesive normal stress
Cohesive normal displacement
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The research was supported by Iran’s National Elites Foundation. The authors would like to thank Prof. Farzam Farahmand, Mr. Behnam Gomari and Mr. Khodadad Azami for their advice and technical support.
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